F86 Medium

Glow-worm F86 Fault Code

The Glow-worm F86 fault code means: your boiler has detected an issue with the sensor or connection for an underfloor heating system, causing it to temporarily lock out to keep your home safe.. It appears on 8 Glow-worm models in our database.

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description: Underfloor heating contact fault; Floor heating contact open; Sensor disconnected or defective
Typical repair cost £90-180 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

Find a Gas Safe engineer

Search the official register for a qualified engineer in your area.

Gas Safe Register →
Boiler cover options

Avoid the next call-out bill

A cover plan would handle faults like F86: no call-out fees, no surprise bills.

Approved partner
Domestic Appliance Guard
Unlimited call-outs, 24/7 helpline, no price-hike promise
Get a quote →

Affiliate links. We may earn a commission at no extra cost to you.

Glow-worm models that show the F86 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Glow-worm F86 fault code information on this page is sourced and cross-checked against the official Glow-worm service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026